The present disclosure relates to an organic Electro Luminescence (EL) display device which emits a light by utilizing an organic EL phenomenon, and a method of manufacturing the same.
A display element having an advanced performance has been required with accelerating development of an information and communication industry. In particular, an organic EL element which attracts attention as a next-generation display device has an advantage that not only a view angle is wide in terms of a spontaneous luminescence type display device and contrast is excellent, but also a response time is fast.
Materials used in a light emitting layer and the like composing the organic EL element are classified into a low-molecular material and a high-molecular material. In general, it is known that the low-molecular material shows a high luminous efficiency and a long life rather than the high-molecular material. In particular, the performance of blue light emission is perceived to be high in the low-molecular material.
In addition, in the case of the low-molecular material, an organic film of the same is generally deposited by utilizing a dry method (evaporation method) such as a vacuum evaporation method. On the other hand, in the case of the high-molecular material, an organic film made of the same is deposited by utilizing either a wet method (application method) such as a spin coating method, an ink-jet method or a nozzle coating method, or a printing method such as a flexo printing method or an offset printing.
The vacuum evaporation method has an advantage that it is unnecessary to dissolve a formation material for an organic thin film into a solvent, and a process for removing the solvent after completion of the deposition is unnecessary. However, the vacuum evaporation has a disadvantage that since it is difficult to carry out the deposition appropriately using a metal mask, and especially, equipment and manufacturing cost in manufacturing of a large panel is high, the application of the vacuum evaporation to a large screen substrate is difficult and the vacuum evaporation has trouble with mass production as well. Then, the application method with which the large area promotion of the display screen is selectively easy attracts attention.
In recent years, a method of depositing a soluble low-molecular material by utilizing the wet method has been searched for. Also, in this case, materials used in the light-emitting layer which show the high luminous efficiency and life characteristics in red and green light emitting layers have been reported. This technique, for example, is described in a non-patent literary document of IMID/IDMC/ASIA DISPLAY 2010 DIGEST 159. However, in the blue light emitting layer deposited by utilizing the wet method, the emission luminance and the life characteristics have been poor irrespective of the low-molecular material and the high-molecular material. In particular, the patterning by the wet method has been perceived to be difficult.
In order to cope with this situation, there is developed a display device in which layers in and after a blue light emitting layer are formed on upper portions of a red light emitting layer and a green light emitting layer obtained through patterning made by either utilizing the application method described above or a transferring method using light radiation such as laser by utilizing a vacuum evaporation method. The adopting of such a structure results in that it is unnecessary to carry out the patterning for the blue light emitting layer, and thus the possibility for scaling-up becomes high.
On the other hand, an additional improvement point in the organic EL element includes a luminous efficiency. Recently, an organic EL element using a phosphorescence material as a luminescence material has been reported. The phosphorescence material has an internal quantum efficiency of 75% or more, theoretically, a value near 100%. Thus, it is expected that the use of the phosphorescence material results in obtaining of the organic EL element having a high efficiently and low power consumption. For example, Japanese Patent Laid-Open No. 2006-140434 discloses a display device in which a blue light emitting layer is formed as a common layer on an upper portion of a light emitting layer including a phosphorescence luminescent material and provided every element.